Postfwd is a policy server that combines complex Postfix restrictions
in a ruleset similar to those of most firewalls. Postfwd
uses the Postfix policy delegation protocol to control access to
the mail system before a message has been accepted. It allows you
to choose an action (e.g. reject, dunno) for a combination of several
SMTP parameters (like sender and recipient address, size or the
client's TLS fingerprint).
